First-principles study of electro-structural, mechanical, optical, and thermal properties of hexagonal chalcogenide perovskites CsTaX3 (X = S, Se)

Abstract

This study presents a comprehensive investigation of the structural, electronic, elastic, optical, and thermoelectric properties of hexagonal chalcogenide perovskites CsTaX₃ (X = S, Se) using first-principles Density Functional Theory (DFT) calculations. Structural optimization using the GGA-PBE functional yields lattice constants of a = 7.44 Å, c = 6.01 Å for CsTaS₃, and a = 7.71 Å, c = 6.14 Å for CsTaSe₃. Both compounds exhibit indirect band gaps, refined using the TB-mBJ potential, with values of 0.90 eV (CsTaS₃) and 0.41 eV (CsTaSe₃). Elastic constants satisfy the Born stability criteria, and calculated bulk moduli are 52.52 GPa (CsTaS₃) and 46.08 GPa (CsTaSe₃), confirming mechanical stability. Optical properties indicate high dielectric constants, with static ε₁ values reaching 6.03 (CsTaS₃) and 8.06 (CsTaSe₃), and strong absorption in the visible region. Thermoelectric analyses reveal positive Seebeck coefficients throughout the 50–1200 K temperature range, indicating p-type conductivity, CsTaSe₃ exhibits a power factor of 1.85 × 10¹¹ W/m·K² and a maximum ZT of 0.75, compared to 1.67 × 10¹¹ W/m·K² and ZT = 0.76 for CsTaS₃. These findings underscore the potential of CsTaS₃ for high-temperature thermoelectric applications and suggest the viability of CsTaX₃ compounds in future energy conversion and optoelectronic technologies.